Dexamethasone inhibits the release of TSH from the rat anterior pituitary gland in vitro by mechanisms dependent on de novo protein synthesis and lipocortin 1

1995 ◽  
Vol 147 (3) ◽  
pp. 533-544 ◽  
Author(s):  
A D Taylor ◽  
R J Flower ◽  
J C Buckingham
Keyword(s):  
Protein Synthesis ◽  
Pituitary Gland ◽  
Outer Surface ◽  
Anterior Pituitary ◽  
De Novo ◽  
Anterior Pituitary Gland ◽  
Pronounced Increase ◽  
Pituitary Tissue ◽  
Dependent Mechanism

Abstract Glucocorticoids have been shown repeatedly to inhibit the secretion of TSH in experimental animals and in man but their site and mode of action are unknown. In the present study, we have used an in vitro model to examine the effects of dexamethasone on the resting and pharmacologically evoked secretion of TSH by the rat anterior pituitary gland, and to show how they are influenced by inhibitors of RNA/protein synthesis. In addition, we have investigated the potential role of lipocortin 1 (LC1), a protein shown previously to contribute to glucocorticoid action in several systems, as a mediator of the glucocorticoid-induced suppression of TSH release in our in vitro preparation. The significant (P<0·01) increases in the release of immunoreactive (ir)TSH from rat anterior pituitary tissue initiated by submaximal concentrations of TRH (10 nmol/l), vasoactive intestinal polypeptide (VIP, 10 nmol/l) or the adenyl cyclase activator, forskolin (100 μmol/l) were reduced significantly (P<0·05) by preincubation of the tissue with dexamethasone (0·1 μmol/l). In contrast, irTSH secretion evoked by a submaximal concentration of the L-Ca2+ channel opener BAY K8644 (10 μmol/l) was unaffected by the steroid, although readily antagonised (P<0·01) by nifedipine (1–100 μmol/l). Inclusion of actinomycin D (1·78 μmol/l) or cycloheximide (0·8 μmol/l), inhibitors of RNA and protein synthesis respectively, in the medium effectively abrogated the inhibitory effects of dexamethasone (0·1 μmol/l) on the secretory responses to TRH (10 nmol/l), VIP (10 nmol/l) and forskolin (100 μmol/l). LC1 was readily detectable by Western blotting in protein extracts of freshly excised anterior pituitary tissue. A small proportion of the protein was found to be attached to the outer surface of the cells where it was retained by a Ca2+-dependent mechanism. Exposure of the tissue to dexamethasone (0·1 μmol/l) caused a pronounced increase in the amount of cellular LC1 attached to the outer surface of the cells and a concomitant decrease in the intracellular LC1 pool. Progesterone (0·1 μmol/l) and aldosterone (0·1 μmol/l) were also weakly active in this regard, but thyroxine and tri-iodothyronine (0·1 μmol/l) were not. Addition of an N-terminal LC1 fragment, LC1(1–188) (0·05–0·53 pmol/l) to the incubation medium reduced significantly (P<0·01) the increases in irTSH release induced by TRH (10 nmol/l), VIP (10 nmol/l) and forskolin (100 μmol/l), but failed to influence (P<0·05) those initiated by BAY K8644 (10 μmol/l). Furthermore, the inhibitory actions of dexamethasone (0·1 μmol/l) on the release of irTSH provoked by TRH (10 nmol/l), VIP (10 nmol/l) and forskolin (100 μmol/l) were substantially reversed (P<0·01) by a specific monoclonal anti-LC1 antibody, while an isotype-matched control antibody was without effect. The results show clearly that dexamethasone, a semisynthetic glucocorticoid, acts at the pituitary level to inhibit the neurochemically evoked release of irTSH. They also provide novel evidence that the inhibitory actions of the steroid are dependent upon de novo RNA/protein synthesis and that they involve an LC1 dependent mechanism. Journal of Endocrinology (1995) 147, 533–544

Alteration by thyrotrophin-releasing hormone of heterogeneous components associated with thyrotrophin biosynthesis in the rat anterior pituitary gland

1984 ◽  
Vol 103 (2) ◽  
pp. 165-171 ◽  
Author(s):  
M. Mori ◽  
M. Murakami ◽  
T. Iriuchijima ◽  
H. Ishihara ◽  
I. Kobayashi ◽  
...  
Keyword(s):  
Protein Synthesis ◽  
Pituitary Gland ◽  
Anterior Pituitary ◽  
De Novo ◽  
Close Association ◽  
Anterior Pituitary Gland ◽  
Male Rats ◽  
Thyrotrophin Releasing Hormone ◽  
Releasing Hormone ◽  
Pituitary Glands

ABSTRACT An influence of thyrotrophin-releasing hormone (TRH) on TSH heterogeneity in close association with de-novo biosynthesis was studied in rat anterior pituitary glands. Hemipituitary glands from adult male rats were incubated in Krebs–Henseleit–glucose media containing [3H]glucosamine and [14C]alanine for 3 and 6 h in the presence or absence of 10 ng TRH per ml. Fractions of TSH in the pituitary extracts were obtained using affinity chromatography coupled with an anti-rat TSH globulin. These TSH fractions were analysed by isoelectric focusing. The control pituitary glands were composed of four component peaks (isoelectric point (pI) 8·7, 7·8, 5·3 and 2·5) of [3H]glucosamine and [14C]alanine incorporated into TSH, and the amounts of radioactivity of these components were increased with the incubation time. Of these peaks, radioactive components of pI 8·7 and 7·8 coincided with the non-radioactive TSH components measured by radioimmunoassay. Addition of TRH increased incorporation of [14C]alanine into TSH in each of the components to a greater extent than that of [3H]glucosamine. In addition, new components with pI 7·2, 6·5 and 6·2, each component corresponding to each unlabelled TSH component, were demonstrated in the presence of TRH. Because addition of TRH did not change the amounts of [14C]alanine-labelled TSH in the media, the newly formed components were assumed to be connected with protein synthesis occurring in the anterior pituitary gland, which may be specific substances in response to TRH administration. These results indicate that TRH principally elicits an increase in protein synthesis in TSH at the anterior pituitary level, resulting in an alteration of TSH heterogeneity. J. Endocr. (1984) 103, 165–171

Effect of hypothalamic neuropeptides on corticotrophin release from quarters of rat anterior pituitary gland in vitro

1984 ◽  
Vol 100 (2) ◽  
pp. 219-226 ◽  
Author(s):  
S. A. Nicholson ◽  
T. E. Adrian ◽  
B. Gillham ◽  
M. T. Jones ◽  
S. R. Bloom
Keyword(s):  
Pituitary Gland ◽  
Anterior Pituitary ◽  
Low Dose ◽  
Physiological Role ◽  
Anterior Pituitary Gland ◽  
High Concentration ◽  
Response Curves ◽  
Corticotrophin Releasing Factor ◽  
Basal Release

ABSTRACT The effect of six hypothalamic peptides on the basal release of ACTH and that induced by arginine vasopressin (AVP) or by ovine corticotrophin releasing factor (oCRF) from fragments of the rat anterior pituitary gland incubated in vitro was investigated. Dose–response curves to AVP and to oCRF were obtained, and the response to a low dose of oCRF was potentiated by a low dose of AVP. Basal release of ACTH was not affected by any of the peptides in concentrations in the range 10−12 to 10−6 mol/l, and only substance P (SP) and somatostatin (SRIF) inhibited significantly the response to oCRF in a dose-related manner. The responses to a range of doses of oCRF or AVP were reduced by 10−8 and 10 − 6 mol SP or SRIF/1, and to a greater extent by the higher dose. Except in the case of 10−6 mol SRIF/1 on the response to AVP, the response was not further diminished by preincubation of the tissue with the peptide before the stimulating agent was added. The inhibition of the responses to AVP or oCRF by 10−9 mol SP/1 was not potentiated by its combination with either 5 × 10−10 or 10−8 mol SRIF/1; the inhibitory effects were merely additive. The results suggest that although SRIF and SP are able to modulate the release of ACTH from the anterior pituitary gland, they do so only at a high concentration. In the case of SRIF these concentrations are several orders of magnitude higher than those reported to be present in the hypophysial portal blood and therefore a physiological role for this peptide in the control of ACTH secretion is unlikely. J. Endocr. (1984) 100, 219–226

scholarly journals Intercellular communication in the rat anterior pituitary gland: an in vivo and in vitro study

1975 ◽  
Vol 67 (2) ◽  
pp. 469-476 ◽  
Author(s):  
WH Fletcher ◽  
NC Anderson ◽  
JW Everett
Keyword(s):  
Pituitary Gland ◽  
Anterior Pituitary ◽  
Hormone Secretion ◽  
In Vitro Study ◽  
Anterior Pituitary Gland ◽  
Stimulus Secretion Coupling ◽  
Unpublished Observation ◽  
Cellular Ca

The concept of "stimulus-secretion coupling" suggested by Douglas and co-workers to explain the events related to monamine discharge by the adrenal medulla (5, 7) may be applied to other endocrine tissues, such as adrenal cortex (36), pancreatic islets (4), and magnocellular hypothalamic neurons (6), which exhibit a similar ion-dependent process of hormone elaboration. In addition, they share another feature, that of joining neighbor cells via membrane junctions (12, 26, and Fletcher, unpublished observation). Given this, and the reports that hormone secretion by the pars distalis also involves a secretagogue-induced decrease in membrane bioelectric potential accompanied by a rise in cellular [Ca++] (27, 34, 41), it was appropriate to test the possibility that cells of the anterior pituitary gland are united by junctions.

scholarly journals In Vivo and In Vitro Arsenic Exposition Induces Oxidative Stress in Anterior Pituitary Gland

2016 ◽  
Vol 35 (4) ◽  
pp. 463-475 ◽  
Author(s):  
Sonia A. Ronchetti ◽  
María S. Bianchi ◽  
Beatriz H. Duvilanski ◽  
Jimena P. Cabilla
Keyword(s):  
Oxidative Stress ◽  
Pituitary Gland ◽  
Anterior Pituitary ◽  
Inorganic Arsenic ◽  
Anterior Pituitary Gland ◽  
Pituitary Cells ◽  
Prolactin Release ◽  
Stress Responsive Genes

Inorganic arsenic (iAs) is at the top of toxic metalloids. Inorganic arsenic-contaminated water consumption is one of the greatest environmental health threats worldwide. Human iAs exposure has been associated with cancers of several organs, neurological disorders, and reproductive problems. Nevertheless, there are no reports describing how iAs affects the anterior pituitary gland. The aim of this study was to investigate the mechanisms involved in iAs-mediated anterior pituitary toxicity both in vivo and in vitro. We showed that iAs administration (from 5 to 100 ppm) to male rats through drinking water increased messenger RNA expression of several oxidative stress-responsive genes in the anterior pituitary gland. Serum prolactin levels diminished, whereas luteinizing hormone (LH) levels were only affected at the higher dose tested. In anterior pituitary cells in culture, 25 µmol/L iAs significantly decreased prolactin release in a time-dependent fashion, whereas LH levels remained unaltered. Cell viability was significantly reduced mainly by apoptosis evidenced by morphological and phosphatidylserine externalization studies. This process is characterized by early depolarization of mitochondrial membrane potential and increased levels of reactive oxygen species. Expression of some key oxidative stress-responsive genes, such as heme oxygenase-1 and metallothionein-1, was also stimulated by iAs exposure. The antioxidant N-acetyl cysteine prevented iAs-induced effects on the expression of oxidative stress markers, prolactin release, and apoptosis. In summary, the present work demonstrates for the first time that iAs reduces prolactin release both in vivo and in vitro and induces apoptosis in anterior pituitary cells, possibly resulting from imbalanced cellular redox status.

Degradation of Insulin-I131 by an Extract of Anterior Pituitary Gland

1958 ◽  
Vol 193 (3) ◽  
pp. 476-478 ◽  
Author(s):  
H. T. Narahara ◽  
R. H. Williams
Keyword(s):  
Pituitary Gland ◽  
Anterior Pituitary ◽  
Trichloroacetic Acid ◽  
Electrophoretic Analysis ◽  
Anterior Pituitary Gland ◽  
Radioactive Material ◽  
Incubation Mixture ◽  
Pituitary Extract ◽  
Insulin Molecule

When insulin-I131 was incubated at 37°C and pH 7.5 with an extract of beef anterior pituitary, the radioactive material was rendered more soluble in trichloroacetic acid (TCA). Electrophoretic analysis of the TCA-soluble reaction product revealed that it was not free iodide. The concept that pituitary extract might contain a system capable of attacking the insulin molecule was strengthened by the observation that the addition of nonlabeled insulin to the incubation mixture decreased the rate of degradation of insulin-I131. The degradative system of beef anterior pituitary extract was found to be nondialyzable and heat-labile. The degradation of insulin by pituitary extracts may help to explain the observation of other workers that such extracts can inactivate insulin in vitro.

Characteristics of Action of Prostaglandins on Cyclic AMP Accumulation in Rat Anterior Pituitary Gland

1975 ◽  
Vol 53 (4) ◽  
pp. 455-460 ◽  
Author(s):  
Pierre Borgeat ◽  
Fernand Labrie ◽  
Pierre Garneau
Keyword(s):  
Cyclic Amp ◽  
Pituitary Gland ◽  
Incubation Medium ◽  
Anterior Pituitary ◽  
Complete Removal ◽  
Anterior Pituitary Gland ◽  
Pituitary Hormone ◽  
Maximal Effect ◽  
Cyclic Amp Accumulation

Prostaglandins (PGs) were found to lead to a marked stimulation of cyclic AMP accumulation in rat anterior pituitary gland in vitro in the following decreasing order of potency: [Formula: see text]. The effect of PGs is potentiated by theophylline. The stimulatory effect of PGs on cyclic AMP accumulation is already detected 2 min after the addition of 1 × 10−7 to 1 × 10−6 M PG E2 and its maximal effect is reached after approximately 30 min of incubation, with a progressive decrease toward basal cyclic AMP levels at later time intervals. Increased intracellular cyclic AMP concentrations are accompanied by an increased release of the nucleotide into the incubation medium. Complete removal of Ca2+ from the incubation medium by addition of EGTA was found to increase the stimulatory effect of PG E2 on cyclic AMP accumulation. The action of PGs on hormonal release and cyclic AMP accumulation support the hypothesis of a role of PGs in the mechanism of anterior pituitary hormone (particularly growth hormone) release.

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